SV27 Series Pilot Operated Check Sensing Valves Installation Instructions

Overview

The ROSS Controls SV27 Series Pilot Operated (PO) Check Sensing Valves are premium-quality inline poppet valves combining pilot operated check functionality with pressure sensing capability. Designed for Category 2 and Category 3 pneumatic safety applications (not for mechanical stamping presses), these valves provide both directional flow control through the PO check mechanism and pressure sensing feedback via the integral auxiliary port.

The PO check sensing valve configuration (document SS281) builds on the base SV27 Series platform, adding pilot operated check functionality that allows free flow from outlet to inlet when the pilot signal is applied, while blocking reverse flow in the absence of a pilot signal. This is valuable in applications where actuators must be held in position by pneumatic pressure while also requiring safety monitoring of the pressure condition.

ROSS Controls, founded in 1921, has been producing fluid power safety valves for over 100 years. Additional technical documentation and distributor information are available at www.rosscontrols.com.

Key Features

Pilot Operated Check (PO Check) Functionality

The pilot operated check valve function allows free flow through the valve in the normal direction, while blocking reverse flow in the absence of a pilot signal. When a pilot signal is applied, the check is opened, allowing reverse flow — enabling cylinder retraction or pressure relief when commanded by the control system. This functionality is integrated directly into the SV27 Series poppet valve design.

Integrated Pressure Sensing with Auxiliary Port

The SV27 PO Check Sensing Valve includes the same auxiliary 1/8 NPT port connected to the outlet (Port 2) as the standard SV27 Series. This port accepts an optional ROSS pressure indicator (Part No. 988A30) or pressure switch kit (Part No. 608A86) to provide real-time feedback on the outlet pressure condition to the machine control system.

Category 2 and 3 Safety Performance

Like the standard SV27 Series, the PO Check version achieves Category 2 PL d per ISO 13849-1. Key functional safety data: B10D Valve 20,000,000; Switch 2,000,000; PFHD 2.35×10⁻⁷; MTTFd 98.15 years (n: 7360); DC 90% for PO Check valves (obtained by monitoring safety switch status). Testing of switch function and sealing is recommended every 8 hours for load holding applications.

Technical Specifications

Safety Category: Category 2 PL d; Category 3 (not for mechanical stamping presses)
Construction: Poppet (Pilot Operated Check configuration)
Mounting Type: In-Line
Flow Media: Filtered air
Ambient Temperature: 40° to 120°F (4° to 50°C)
Media Temperature: 40° to 175°F (4° to 80°C)
Inlet Pressure: 40 to 150 psig (2.8 to 10.3 bar)
Pilot Pressure: Must be equal to or greater than inlet pressure
Solenoid: AC or DC power; rated for continuous duty
Standard Voltages: 24 VDC; 110–120 VAC, 50/60 Hz
CNOMO Style Power Consumption: 11 VA inrush, 8.5 VA holding; 6 watts DC
Pacer Style Power Consumption: 87 VA inrush, 30 VA holding; 14 watts DC
Switch Current/Voltage Max.: 2.5 A / 120 VAC
Switch Current/Voltage Min.: 50 mA / 24 VDC
Functional Safety: B10D Valve 20,000,000; Switch 2,000,000; PFHD 2.35×10⁻⁷; MTTFd 98.15 years
DC (PO Check valves): 90% by monitoring safety switch status
Auxiliary Port: 1/8 NPT at outlet (Port 2) for pressure indicator or switch
Application Limitation: Not for mechanical stamping press clutch/brake control

Applications

Load Holding with Pressure Verification

The SV27 PO Check Sensing Valve is ideally suited for load holding applications where a cylinder or actuator must maintain position under load, with the ability to verify that the required holding pressure is present. The PO check blocks reverse flow (and thus unintended actuator movement) while the pressure sensing port confirms that holding pressure is maintained, providing both physical protection and electronic verification.

Safety Circuit Pressure Monitoring

In Category 2 and 3 safety circuits, the SV27 PO Check Sensing Valve serves as a monitoring point that provides feedback to the safety control system. The pressure switch kit (608A86) outputs a signal that can be monitored by a safety PLC or safety relay to detect loss of holding pressure, triggering a safety stop if pressure drops below the required threshold.

Safety and Compliance Standards

ISO 13849-1 — Category 2 PL d compliance
B10D: Valve 20,000,000; Switch 2,000,000
PFHD: 2.35×10⁻⁷
MTTFd: 98.15 years at 7,360 cycles per year
DC (PO Check): 90% by monitoring safety switch status
Testing: 8-hour switch function and sealing test recommended for load holding
Not for mechanical stamping press clutch/brake control

Installation and Setup Guide

Air Line Preparation

Blow all air lines clean before installation. Install a 5-micron rated air filter in the inlet line close to the valve. Verify supply pressure is within the 40 to 150 psig (2.8 to 10.3 bar) operating range.

Valve and Port Connections

Install pipe in valve ports by engaging one turn, applying thread sealant (tape not recommended), then tightening to prevent sealant contamination. For parallel threads, do not use sealant. Ensure adequate supply line size at Port 1 without restrictions.

Pilot Supply Connection

For pressure control: connect a 1/4-inch control line to the air cap port. For solenoid control: pressure is supplied internally for most standard models. External pilot supply models require a 1/8-inch line at port X-1 in the pilot housing at the pressure specified in the valve specifications.

Pressure Sensing and Switch Installation

Install the optional pressure indicator (988A30) or pressure switch kit (608A86) in the auxiliary 1/8 NPT outlet port. Wire the pressure switch contacts to the machine control system. During normal pressurized operation, contacts 1 and 3 are closed (normally open). When depressurized, contacts 1 and 2 are closed (normally closed). Verify switch operation after installation.

Why Choose ROSS Controls

ROSS Controls has over 100 years of fluid power engineering experience. The SV27 PO Check Sensing Valve demonstrates ROSS's ability to combine multiple pneumatic functions — pilot operated check, pressure sensing, and safety monitoring — into a single compact package, reducing circuit complexity and potential failure points. For technical support, contact ROSS at 1-800-GET-ROSS or www.rosscontrols.com.

Download This Document

The official SV27 Series PO Check Sensing Valves Installation Instructions (document SS281) provides complete specifications, installation guidance, and service kit information.

Download PDF: https://ross-admin-global-us-east.s3.amazonaws.com/production/uploads/document_language_file/file/98/ROSS_SV27_Series_PO_Check_Sensing_Valves_Installation_Instructions_SS281.pdf.pdf

Frequently Asked Questions

Q: What is a pilot operated check (PO check) valve?

A: A PO check valve allows free flow in one direction (normal forward flow) but blocks reverse flow unless a pilot signal is applied. When the pilot signal is applied, the check is opened, allowing reverse flow. This is used to hold loads in position when the pilot is not applied.

Q: What is the difference between the SV27 standard and the SV27 PO Check version?

A: The standard SV27 (SS280) is a sensing valve for inline mounting. The SV27 PO Check version (SS281) adds pilot operated check functionality, blocking reverse flow in the absence of a pilot signal while still providing pressure sensing through the auxiliary port.

Q: What diagnostic coverage does the SV27 PO Check achieve?

A: DC for PO Check valves is 90%, obtained by monitoring safety switch status, compared to 99% for 3/2 valves. This reflects the additional complexity of the PO check mechanism.

Q: Can the SV27 PO Check be used for mechanical press control?

A: No. ROSS SV27 Series valves, including the PO Check version, are not designed as control valves for air clutch/brake mechanisms on mechanical power presses. Only double valves conforming to applicable standards should be used for press clutch/brake applications.

Q: What is the recommended test frequency for load holding applications?

A: ROSS recommends testing the switch function and sealing every 8 hours for load holding valve applications to maintain the required functional safety performance per ISO 13849-1.

Q: What pressure switch kit part number should I use with the SV27 PO Check?

A: The optional ROSS pressure switch kit for the SV27 Series is Part No. 608A86. An optional pressure indicator (Part No. 988A30) is also available.

Q: What are the contact states of the pressure switch in normal operation?

A: During normal pressurized operation, contacts 1 and 3 are closed (normally open, switch pressurized). When the pressure drops (lockout or depressurized condition), contacts 1 and 2 close (normally closed).

Q: What compatible lubricants should be used with SV27 Series valves?

A: Although the SV27 Series does not require air line lubrication itself, compatible lubricants (for other mechanisms in the circuit) include petroleum base oils with oxidation inhibitors, aniline point 180°F–220°F (82°C–104°C), ISO 32 or lighter. Avoid phosphate additive oils and diester oils.